body{
    margin: 0;
    padding: 0;
}

body{
    background-color: #000;
}

.box{
    width: 400px;
    height: 400px;
    margin: 200px auto;
    background-color: rebeccapurple;
    box-shadow: 0 0 5px 5px  cornflowerblue;
    transition: .6s;
}